1. Field of the Invention
This invention relates generally to the field of multimedia playback systems. More particularly, the invention relates to a system and method for efficiently decoding, converting and rendering DVD subpicture data on a multimedia playback system.
2. Description of the Related Art
The MPEG-2 standard is one of the most popular audio/video compression standards and is used in a wide range of multimedia applications. For example, MPEG-2 is used as the underlying compression algorithm for both digital cable and satellite broadcast channels and for Digital Versatile Disks (“DVDs”) (also referred to as “Digital Video Disks”). In addition, MPEG-2 is used as the compression algorithm for a vast number of computer-based multimedia applications.
Although the underlying MPEG-2 compression algorithm is similar for each application, the manner in which the compressed audio/video content is packetized, transmitted, stored and otherwise processed varies considerably from one application to the next. For example, cable and satellite companies transmit the MPEG-encoded channels within a multiplexed “transport streams” comprising transport packets of a fixed 188 bytes in length. Transport streams follow the T-STD (transport system target decoder) model defined in ISO/IEC 13818-1.
By contrast, MPEG content is stored on DVDs in a unique “program stream” format, using packets of 2048 bytes in length. Normal program streams follow P-STD (program stream target decoder) model defined in ISO/IEC 13818-1. The DVD specification defines a new target decoder model, E-STD (extended system target decoder), which is an extension of the P-STD model and which is outside of the MPEG-2 specification. More specifically, the DVD specification defines additional media types and data structures that are stored and transmitted within MPEG data packets but are not part of the MPEG specification including, for example, sub-picture data defining graphics to be displayed on the television/computer screen (e.g., interactive navigation menus, subtitles, overlays, . . . etc), AC-3 audio, Presentation Control Information (“PCI”) used to navigate a play path through DVD multimedia files, and Data Search Information (“DSI”) used to provide different types of playback timing information. In addition, DVD defines a large amount of sideband metadata that is not contained within the MPEG stream itself but which is used to locate content within the DVD given a set of user selections and/or predefined navigation parameters.
As such, DVD players must be equipped with the hardware and/or software capable of decoding these additional media types and metadata in order to create a compliant DVD viewing experience. By contrast, the hardware and/or software used in typical cable and satellite set-top boxes (“STBs”) are only capable of decoding standard MPEG-2 transport streams.
Given the increasing popularity of DVDs and the fact that most users already subscribe to cable and/or satellite services, it would be practical to develop a multimedia system which would allow DVDs and (potentially) other media types to be properly decoded and rendered using a standard transport stream decoder.